The invention relates to an apparatus for continuously removing liquid (dewatering) from flowing suspensions, and a screen assembly utilizable in such apparatus. The invention is of the same general type of dewatering apparatus as shown in U.S. Pat. No. 4,041,560 (the disclosure of which is hereby incorporated by reference herein), wherein a screen body is reciprocated in a direction generally parallel to a suspension flow, with backflushing of the screen openings taking place during movement of the screen opposite to the direction of movement of the suspension.
While prior systems such as disclosed in U.S. Pat. No. 4,041,560 are generally successful in accomplishing their desired results, there are several areas where improvement is possible. The apparatus according to the present invention is advantageous compared to such prior art assemblies in a number of ways. In particular, the apparatus according to the invention has a greater effective screening area for a given design length, can be made much bigger since even when large it will not significantly interfere with the flow pattern of the suspension, and consumes less power since the moveable parts can be of smaller weight and there is less resistance to movement.
According to one aspect of the present invention a screen assembly is provided for an apparatus for continuously dewatering flowing suspensions. The screen assembly includes a screen body having a perforated wall for allowing the passage of liquids therethrough but preventing the passage of particles greater than a predetermined size therethrough. The screen body is elongated in the first direction and has first and second ends, with a first slide bearing mounted to the screen body first end and a second slide bearing mounted to the screen body second end. The second slide bearing is spaced from the screen body perforated wall a distance greater than the distance the first slide bearing is spaced from the screen body perforated wall, and means are attached to the screen body for facilitating attachment of a device for moving the screen body generally in the direction of elongation of the screen body. The screen body perforated wall may define a cylinder side wall, the cylinder being circular in cross-section with the bearings being annular components, and the means facilitating attachment may comprise a connecting sprider mounted to the interior of the perforated cylinder wall.
According to another aspect of the present invention as apparatus is provided for continuously dewatering flowing suspensions, which apparatus includes a generally cylindrical container through which suspension to be dewatered flows in a first direction, the container having an axis extending generally parallel to or concentric with the first direction. Screen means are provided for removal of a portion of liquid from the suspension flowing through the container, and extending generally along the axis of the container in which it is disposed, the screen means comprising a first end and a second end opposite the first end and spaced generally along the axis from the first end. Sealing bearing means are mounted on the first end and the second end of the screen means, respectively, for movement with the screen means and cooperate with first and second bearing surface means, respectively, mounted interiorly of the container. The bearing surface means have different effective cross-sectional areas. The screen means between the first and second ends thereof and the bearing surface means defined a screen cavity volume, and an outlet is provided extending from the screen cavity volume to an area remote from the container. Mechanical means for moving the screen means in the first direction and in a second direction opposite the first direction are provided, so that the cavity volume changes during movement of the screen means to effect backflushing during movement in the second direction.
The screen means and bearing surface means may have a wide variety of shapes and configurations. For instance the screen means may be planar and the bearing means linear and the bearing surface means planar, or the screen means may be cylindrical with the bearing means and bearing surface means annular. Similarly the cylindrical container may have any desired cross-section, including circular and quadrate. Normally the mechanical means moves the screen in the first direction at about the speed at which the suspension flows, and moves the screen in the second direction at a much greater speed.
The apparatus according to the present invention may be used for dewatering a wide variety of suspensions, but is particularly useful for dewatering comminuted cellulosic fiber material suspended in a liquid, which can be either water or a chemical treatment liquid, such suspensions commonly being used and produced during the production of paper products.
It is the primary object of the present invention to provide an approved apparatus, and components therefor, for continuously dewatering flowing suspensions. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.